1. Field of the Invention
The invention relates to gas chromatography-mass spectrometry (GC-MS) instrument and more particularly to a method of switching ports of a switching valve of a GC-MS apparatus.
2. Description of Related Art
A conventional gas chromatography-mass spectrometry (GC-MS) apparatus is shown in FIG. 1 and comprises a sample injector 1, a heart-cutting unit 3 for separating gaseous compounds carried by carrier gas from the sample injector 1 into different fractions, a first capillary column 2 interconnecting the sample injector 1 and the heart-cutting unit 3, a flame ionization detector (FID) 7, an interconnecting column 4 interconnecting the FID 7 and the heart-cutting unit 3, a mass spectrometer (MS) 6, and a second capillary column 5 interconnecting the heart-cutting unit 3 and the MS 6. The FID 7 can be replaced with nitrogen-phosphorous detector (NPD) or one of similar detectors.
However, a number of drawbacks have been found in the conventional GC-MS apparatus. In detail, as sample gaseous compounds are preliminarily separated by the first capillary column 2 into different fractions, through setting different time slot and carrier gas pressure of the heart-cutting unit 3, the simple compounds with good separation separated by the first capillary column 2 are to be sent to a detector such as FID or NPD via the interconnecting column 4 for analysis while the complex compounds which are not separated from each other completely and cannot be further separated from each other by the first capillary column 2, are required to be sent to the second capillary column 5, which are of different solid phase from that of the first capillary column 2, for further separation before being sent to the MS 6 for quantitative and qualitative analysis. The simple compounds detected by the detector FID or NPD from a conventional GC-MS will only be able to be resulted in a quantitative analysis while no qualitative analysis as regards the name, structure, CAS No., etc. of such simple compounds may be concluded, thus causing inconvenience to the user. That is, different fractions cannot be sent to the MS 6 at the same time for analysis. Adding another MS to the GC-MS device can solve the problem but it will increase cost. Further, relevant software is required for control purposes.
Thus, the need for improvement still exists.